Few people, especially beginners, will have no difficulties at all with the meditation practice.

Aches and pains are one of the major distractions. They can be addressed by preparing for them prior to the retreat, using the hot springs, sitting in an appropriate way, and treating them as meditation objects.

Inconsiderate noise, and other distractions caused by people can seem to be to blame. Merely continue to be mindful of what you are doing. You cannot influence what anyone else is doing in any way except by allowing them to observe your right effort.

Distractions caused by mosquitos and other creepy-crawlies should be treated in the same way. Just continue to be mindful of what you are doing.

Loss of concentration, through tiredness or intrusion of thoughts can be frustrating. This is part of the meditation experience, and these things will happen. Try to continually return the focus of concentration to the breath and accept the distraction. Becoming angry at yourself for not practicing tightly enough will not help you.

Some days will be good days, and other days will just be difficult ones. Though there is always a root cause of this but it's not really important. It's just a distraction and will only affect your meditation practice if you chose to let it.

In short, everything is just a distaction. Things come into awareness, remain for a length of time, whether short or long, and then they stop. You react in a certain way and can either chose to hold onto that reaction and let it affect you, or let it naturally fade away and continue with your practice.